The present invention relates to a brushless motor driving device of the sensorless type so configured to detect a rotor position fry use of an induced voltage generated across an armature coil.
In the brushless motor driving device of the sensorless type, when a rotor is in a stationary condition, since no induced voltage generates across an armature coil, it is not possible to detect a rotor position. Therefore, when the motor is started, it becomes necessary to forcibly give a rotating magnetic field from the outside at the time of starting the motor. A brushless motor driving device having a means for this purpose is proposed in for example Japanese Patent Application Pre examination Publication No. JP-A-57-173385.
Now, the brushless motor driving device disclosed in JP-A-57-173385 will be described with reference to FIG. 14. In the drawing, a power supply 1 is connected through a power switch 2 to each of a U-phase coil, a V-phase coil and a W-phase coil of armature coils 3 of a three-phase brushless motor and to a fixed timer circuit 4. The armature coils 3 are located to surround a rotor 10. The U-phase coil, the V-phase coil and the W-phase coil of the armature coils 3 are connected to a collector of transistors TR1, TR2 and TR3, respectively, which are included in a driver circuit 9. An emitter of these transistors TR1, TR2 and TR3 are connected to ground. An output S1 of the fixed timer circuit 4 is connected to a switching timer circuit 5 and a rotating magnetic field generating circuit 6, and an output S2 of the switching timer circuit 5 is connected to a switch circuit 7 for controlling the switch circuit 7. An induced voltage detecting circuit 8 has inputs connected to the U-phase coil, the V-phase coil and the W-phase coil of the armature coils 3, respectively, for detecting an induced voltage generated on the respective phase coils of the armature coils 3. This switch circuit 7 receives, from the rotating magnetic field generating circuit 6, currents S3, S4 and S5 for driving the driver circuit 9. The switch circuit 7 also receives, from the induced voltage detecting circuit 8, a drive current based on the induced voltage detected from the respective phase coils of the armature coils 3. The switch circuit 7 is controlled by the switching timer circuit 5 to select one of the received drive currents so as to supply the selected drive current to the driver circuit 9. Three output terminals of the switch circuit 7 are connected to a base of the transistors TR1, TR2 and TR 3, respectively.
With this arrangement, when the power switch 2 is turned on, one end of each of the U-phase coil, the V-phase coil and the W-phase coil of the armature coils 3, is connected the power supply 1. Simultaneously, the fixed timer circuit 4 operates to generate the control signal S1 having a constant time width shown at (a) in FIG. 15 for exciting one phase coil of the armature coils 3, for example, the W-phase coil. This control signal S1 is supplied to the rotating field generating circuit 6, and at the same time, to the switching timer circuit 5. When a constant time elapses after the control signal S1 is outputted from the fixed timer circuit 4, the fixed timer circuit 4 is brought into an off condition. Thus, the rotating magnetic field venerating circuit 6 generates the drive signals S3, S4 and S5 as shown at (c), (d) and (e) in FIG. 15, respectively, for exciting the U-phase coil, the V-phase coil and the W-phase coil of the armature coils 3. The drive signals S3, S4 and S5 are supplied through the switch circuit 7 S to the base of the transistors TR1, TR2 and TR3, respectively. The switch circuit 7 is controlled by the switching signal S2 at (b) in FIG. 15 outputted from the switching timer circuit 5, so that switches in the switch circuit 7 are putted in a connection condition shown in FIG. 14. This connection condition is maintained until the switching signal S2 is brought into a low level.
The drive signals S3, S4 and S5 generated in the rotating magnetic field generating circuit 6 are sequentially supplied to the base of the transistors TR1, TR2 and TR3, respectively, so that an electric current supplied from the power supply 1 sequentially flows in the U-phase coil, the V-phase coil and the W-phase coil of the armature coils 3, respectively, with the result that a rotating magnetic field is generated in the armature coils 3 so that the rotator starts to rotate. Thus, if use motor is started and if the predetermined time has elapsed, the switching signal S2 outputted from the switching timer circuit 5 is brought into the low level, so that the connection condition of the switch circuit 7 is changed from a condition opposite to the connection condition shown in FIG. 14. As a result, the drive signals outputted from the induced voltage detecting circuit 8 by detecting an induced voltage generated an the respective phase coils of the armature coils 3, are supplied through the switch circuit 7 to the drive circuit 9 so as to sequentially drive the transistors TR1, TR2 and TR3, whereby rotation of the three-phase brushless motor is maintained.
However, since the drive signals generated by the rotating magnetic field generating circuit 6 have a constant pulse width, when the motor is started, a phase exciting time becomes constant, so that a time required for starting becomes long, or alternatively, the motor cannot he started smoothly. Furthermore, the phase exciting time and the operating time of the fixed timer circuit 4 are fixed and therefore, cannot be changed arbitrarily.
Accordingly, it is an object of the present invention to provide to brushless motor driving device which has overcome the above mentioned problems of the prior art.
Another object of the present invention is to provide a brushless motor driving device capable of shortening the starting time and also of smoothly starting the motor.
Still another object of the present invention is to provide a brushless motor driving device capable of arbitrarily setting the exciting time at the time of starting the motor.
The above and other objects of the present invention are achieved in accordance with the present invention by a brushless motor driving device so configured to control excitation of each phase armature coil on the basis of starting patterns supplied from a start circuit in a starting operation and a rotator position signal obtained from an induced voltage generated between opposite ends of each phase armature coil after completion of the starting operation, thereby to rotate a rotator, wherein the start circuit includes a main counter generates a pulse at each time the main counter counts a clock signal to a variable full count value, a sub counter counts the pulse generated by the main counter, the variable full count value being subtracted by a count value of the sub counter, and a start pattern generating circuit generating starting pattern in response to the pulse generated by the main counter.
In an embodiment of the brushless motor driving device, the sub counter is of m bits and the main counter is of n bits where m less than n, and only m MSB bits of the full count value in the main counter is variable.
Specifically, the main counter includes n flipflops connected to constitute a counter of n bits, a plurality of AND circuits each receiving an output of different flipflops of the n flipflops, and a plurality of selector circuits connected between an output of selected flipflops of the n flipflops and the AND circuits, and the sub counter includes m flipflops connected to constitute a counter of m bits. Each of the selector circuits receives a corresponding one bit of the m MSB bit, of the main counter and a fixed logical level and is controlled by a corresponding one of the m bits of the sub counter to output the corresponding one bit of the in MSB bits of the main counter when the corresponding one of the m bits of the sub counter is at a first logic level and the fixed logical level when the corresponding one of the m bits of the sub counter is at a second logic level.
The brushless motor driving device can further includes a low rotation detecting circuit for detecting that a rotation speed of the rotor does not reach a predetermined value, and a switch circuit controlled by a low rotation detection signal outputted from the low rotation detecting circuit to switch from the starting pattern to the rotor position signal when the rotation speed of the rotor reaches the predetermined value.
The above and other objects, features and advantages of the present invention will be apparent from the following description of preferred embodiments of the invention with reference to the accompanying drawings.